The American Forestry Association urged Congress yesterday to pass tougher air-pollution laws to protect the nation's forests, saying that the risks of delay outweigh the costs of additional regulations.

The association is the first national forestry organization to endorse broad new emission controls, joining a chorus of conservation groups and scientists whose main concern is acid rain. The forestry association is a citizens' organization that usually works closely with timber industry groups.

"There is little scientific doubt in our mind that acid rain is damaging the forest ecosystem," said R. Neil Sampson, executive vice president. He said, however, that the association wants Congress to address a "broad array" of pollutants, not just the sulfur dioxide and nitrogen oxides linked to acid rain.

"Although acid rain has been at the center of the debate, our research indicates that this is too narrow a focus to accurately address air pollution's full threat to forests," Sampson said.

A forestry association task force concluded that trees may be suffering more severe damage from pollution problems other than acid rain, including toxic metals leached from the soil and ozone formed by hydrocarbons.

The association's new position puts it at odds with trade groups representing the timber industry, including the American Paper Institute and the National Forest Products Association. John A. Thorner, environmental counsel for both groups, said yesterday that the industry sees "no convincing evidence that controlling air pollution on a national scale will improve the health of the forests."

The industry believes there is "no imminent crisis" and supports continued air-quality research, he said.

But David W. Schindler, a research scientist at the Freshwater Institute in Canada and an adviser to the forestry association task force, said that scientists may have underestimated the speed with which manmade pollutants are altering aquatic and forest systems.

"What we see is running far ahead of what scientists were predicting 10 years ago," he said. "Ecologists have been far too conservative in their projections."